Tea filter pack for automatic brewers

ABSTRACT

A conformable, self-aligning, high extraction efficiency tea filter pack capable of flavor extraction efficiencies comparable to those obtained using an identical quantity of bulk tea leaves and a paper filter under identical brewing conditions, but which exhibits substantially consistent pot-to-pot brew strength for any given automatic drip coffee maker. The preferred filter pack is formed from two layers of flexible material which are secured to one another about their outermost periphery with a predetermined quantity of tea leaves housed within a brew chamber formed between the two layers. The brew chamber exhibits a maximum volume between about 100 percent and about 400 percent greater than the volume of the dry tea leaves contained therein. The discharge flow rate from the brew chamber is slower than the inlet flow rate into the brew chamber to permit a buildup of water and flooding of the brew chamber. The flexible conformable sidewall surrounding the brew chamber extends upwardly a vertical distance which is at least sufficient to capture enough hot water to totally immerse the brew chamber when the brew chamber is in its fully expanded condition. This causes the tea leaves within the chamber to expand and float throughout the remaining portions of the brew cycle, thereby establishing a steady state brewing condition which is highly effective in maximizing tea/water contact as the hot water passes through the brew chamber on its way to the pot.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 08/084,051filed on Jun. 29, 1993, now abandoned, which is a continuation-in-partof U.S. patent application Ser. No. 07/907,761, filed Jun. 30, 1992, nowU.S. Pat. No. 5,298,267, which is a continuation-in-part of U.S. patentapplication Ser. No. 07/726,429, filed Jul. 5, 1991, now abandoned.

FIELD OF THE INVENTION

This invention relates to low cost, high efficiency, disposable teafilter packs to be used with most commercial drip coffee makers.

BACKGROUND OF THE INVENTION

In order to avoid purchasing a specialized, dedicated tea brewingmachine, many consumers and institutions have attempted to utilize theirautomatic drip coffee machines to brew tea. It is estimated that nearly25% of all iced tea served in restaurants and away from home is brewedwith automatic drip coffee machines.

A typical coffee brew machine comprises a base member with a heaterelement used to support a glass coffee pot and a coffee filter holderattached to the base in the position above the coffee pot. The coffeefilter holder is typically frusto-conical in shape with one or morecentral apertures through the bottom wall and is designed to receive adisposable coffee filter. Many such holders also contain a wire basketor ribbed inner surface within the filter holder to prevent the filterfrom pressing against the solid outer wall of the filter holder. Thisprevents the moistened filter from forming a liquid impervious seal withthe solid outer wall, and ensures that the entire surface of the filteris available for filtering purposes.

The coffee filter is normally fabricated from porous paper and is alsofrusto-conical in shape so as to be received within the coffee filterholder. In use, the coffee filter will be placed in the coffee filterholder and a measured amount of roast and ground coffee is placed in thebottom portion of the coffee filter. A measured quantity of hot water isthen directed into the interior of the coffee filter onto the groundcoffee. As the water passes through, the coffee expands and floats up inthe filter increasing the coffee/water contact area. The water will thenpercolate through the ground coffee and flow through the bottom andlower side portions of the porous coffee filter and through the coffeefilter holder apertures down into the coffee pot.

One disadvantage with attempting to use the aforementioned system forbrewing tea is that the tea leaves must be individually measured into afilter (usually a coffee filter) each time a pot of tea is to be brewed.This is time consuming and may result in too much or too little teabeing placed in the filter. If the amount of tea placed in the filtervaries to any significant extent, then the brew strength of theresultant tea will also vary. Another disadvantage is that separatereceptacles must be provided for the individual filters and the tealeaves. Lastly, when measuring the tea leaves into the filter ordisposing of a used filter, the spent tea leaves are often spilled ontothe counter area or the floor resulting in waste of tea leaves and awaste of time in cleaning up.

Coffee manufacturers have substantially eliminated the pot-to-pot brewstrength inconsistencies arising from poor measurement of coffee by theoperator by providing unitized pouches, each containing a predeterminedvolume of roast and ground coffee suitable for brewing a single pot ofcoffee of reasonably consistent strength from one pot to the next.However, these unitized pouches add to cost and disposal problems due tothe need for additional packaging equipment and material. In addition,they do not eliminate the messiness problems normally associated withbulk coffee/paper filter systems, since loose grounds and filters muststill be disposed of. Corresponding unitized tea pouches have beendeveloped by tea manufacturers, but these fare no better than the coffeepouches in addressing these drawbacks.

Recently, coffee filter packs have been designed in an attempt toovercome some disadvantages from this method. Most of these coffeefilter packs are made with heat sealable filter paper or from non-wovenpolyester, polypropylene, polyethylene or a combination thereof. Thesematerials are typically more expensive than conventional filter paper,which is typically comprised almost entirely of wood fiber. Moreover,these filter packs are usually circular or square in shape and simplycover the bottom wall of the coffee filter holder. These filter packsare often improperly positioned in the coffee filter holder resulting ininconsistent brew strength from pot-to-pot, since their shape andmaterials of construction allow water to escape around the sides andthrough the coffee filter pack without sufficient exposure to all of thecoffee contacted in the brew chamber of the filter pack. This results inpoor coffee extraction. Furthermore, the coffee will often migrate toone side of the filter pack so that much of the water which does passthrough the brew chamber of the filter pack does not contact any coffee.As a result, these filter packs produce brewed coffee with a relativelylow level of extracted flavor solids as well as an inconsistent brewstrength from pot-to-pot.

Experience to date has been that filter packs of the prior art do muchto overcome the messiness of the bulk coffee/filter paper systems theyhave replaced. Unfortunately, they have typically exhibited lowerextraction efficiencies than the bulk coffee/filter paper systems. Inaddition they have typically introduced much worse pot-to-pot brewstrength variation than bulk coffee systems using premeasured unitizedpouches of roast and ground coffee in conjunction with paper filters.

Once again, tea manufacturers have developed corresponding filter packsfor their products. Unfortunately, these tea filter packs incorporatethe same problems which plague the coffee filter packs, and alsoadditional problems which arise due to the differences in brewingcharacteristics between coffee and tea.

In general, tea leaves absorb water and expand to a much greater extentthan roast and ground coffee. Because of this degree of expansion, teafilter packs which allow no more room for expansion than typical coffeefilter packs may in fact rupture if the expanded volume of the tealeaves is greater than the maximum available volume within the teafilter pack. This results in pieces of tea leaves floating loosely inthe brewed tea, and likely passing down through the filter holder andinto the finished product, an undesirable occurrence.

Ground coffee also generally contains a much greater proportion of fine,dust-like particulate material than tea leaves which have been crushedor shredded. When wet, coffee tends to pack more tightly and presents amuch greater obstacle to the passage of water than does a similarquantity of tea leaves. Wet coffee particles also exhibit a much greatertendancy to clog the pores of porous filters than tea leaves. Thisclogging tendancy is in large part the reason coffee brewing machinesincorporate a wire basket or ribbed inner surface inside the filterholder, i.e., to maximize the available filtering area. Tea filter packsthus relying on the flow rate of the coffee maker to control brewingtime will not permit the tea to steep in the hot water for a sufficientamount of time for good extraction, as water will tend to pass toorapidly downwardly through the entire lower surface of the tea filterpack and out through the bottom of the filter holder. This results inpoor extraction efficiency and poor utilization of the tea leaves.

By way of contrast, Applicants have learned that in order to minimizebrew time, maximize flavor solids extraction and make a good pot of tea,a substantial portion of the hot water directed into the filter packmust contact the tea in the brew chamber after a substantially steadystate brewing condition has been established within the brew chamber,i.e., after the brew chamber has been completely flooded with theincoming hot water so that the chamber expands to its maximum volume andallows substantially all of the tea leaves contained therein to looselyfloat within the chamber.

Applicants have further learned that this is preferably done byproviding a substantially water impermeable side wall having a heightwhich is sufficient to retain at least enough water to permit completeimmersion of the brew chamber when the brew chamber is in its fullyexpanded condition in combination with inlet and discharge flow ratesinto and out of the brew chamber that will cause the water to build upand puddle the tea inside the brew chamber. If the water is not allowedto build up inside the brew chamber (as is typically the case with priorart filter packs) or if the tea leaves contained in the brew chamber ofa prior art filter pack have shifted to one side of the brew chamberwhen the prior art filter pack is placed in the filter holder, thefailure to properly control the inlet and outlet flow rates and thefailure to provide a substantially water impermeable side wall having aheight which is sufficient to retain at least enough water to completelyimmerse the brew chamber when the brew chamber is in its fully expandedcondition will allow much of the water to flow directly through oraround the brew chamber of the prior art filter pack without evercontacting any of the tea leaves therein.

In addition, Applicants have learned that the brew chamber must be largeenough to allow the tea leaves enough room to expand and float whilewater is building up in the brew chamber in order to achieve sufficienttea/water contact, i.e., to achieve a steady state brewing condition.This helps to prevent channeling of the water through the filter packwithout sufficient tea/water contact. Minimizing channeling isimportant, since channeling of the hot water directly through the brewchamber without sufficient tea contact results in poor and inconsistenttea flavor solids extraction.

It is therefore an object of the present invention to provide animproved tea filter pack which overcomes many of the problems associatedwith the prior art brewing systems which employ bulk tea leaves anddiscrete paper filters, which approximates the extraction efficiency ofsystems employing bulk tea leaves and discrete paper filters, whichprovides reasonably consistent pot-to-pot brew strength without the needfor premeasured unitized pouches of tea leaves, and which avoids thepot-to-pot brew strength inconsistency typically associated with priorart filter packs.

It is another object of the present invention to provide such animproved tea filter pack which is relatively insensitive to operatorplacement within the filter holder of the coffee machine, which includesa substantially impermeable vertically oriented, conformable side wall,which is made almost entirely of relatively inexpensive flexiblematerial, such as ordinary filter paper, and which can be used with awide range of existing coffee filter holders without any need to modifythem.

SUMMARY OF THE INVENTION

The present invention achieves the desired results by providing animproved tea filter pack of a generally frusto-conical shape, made ofinexpensive flexible material, but having a substantially verticallyextending conformable side wall which is substantially impermeable towater. In order for the hot brewing water to be in highly effectivecontact with the predetermined amount of tea leaves contained in thebrew chamber as it passes therethrough, the brew chamber is constructedso that the flow rate of liquid into the brew chamber is greater thanthe flow rate of liquid out of the brew chamber. Furthermore the filterpack is preferably constructed so that the flow rate at which the coffeemaker delivers the hot brewing water to the filter pack is equal to orless than the rate at which water passes into the brew chamber andgreater than the rate at which brewed tea flows out of the brew chamber.

The substantially water impermeable vertically extending continuous sidewall of improved tea filter packs of the present invention is comprisedof flexible material so that it can automatically conform to the porousfilter support means in the coffee maker regardless of how much care isexercised by the operator in placing the filter pack in the filtersupport means. The substantially water impermeable side wall must behigh enough after placement of the filter pack in the filter supportmeans to capture enough of the incoming hot brewing water so that asubstantially steady state brewing condition is established within thebrew chamber relatively early in the brewing cycle, i.e., a floodedcondition in which the brew chamber has been expanded to substantiallyits maximum volume by the incoming hot water. In addition, the brewchamber of the filter pack must be large enough to allow the tea leavesto expand and loosely float within the flooded chamber in order toestablish a substantially steady state brewing condition within the brewchamber. This means that the substantially water impermeable side wallof the filter pack must extend upwardly a vertical distance which is atleast equal to the maximum vertical height which can be assumed the brewchamber in a fully flooded condition. Otherwise flooding of the brewchamber will not take place. Also, as previously noted, if sufficientinterior volume is not available to accomodate the expanding tea leaves,the filter pack may in fact rupture during the brewing operation.

The higher the substantially water impermeable side wall extends abovethis minimum, the greater will be the filter pack's insensitivity tocareless placement within the filter support means, since lack ofperfect concentricity with the filter support means will not result inan inability to retain enough hot water to establish a flooded steadystate brewing condition within the brew chamber.

As a practical matter, the vertical height of the substantially waterimpermeable side wall is greater than the foregoing minimum to preventoverflow of the incoming hot water from the coffee maker (recall thatthe discharge flow rate of brewed tea from the brew chamber is normallyless than the incoming flow rate of hot water to the filter pack topermit flooding of the brew chamber).

The maximum height of the substantially water impermeable side wall is,of course, limited by the vertical height of the filter support meansused on the coffee makers which are to employ the filter packs inquestion. If the filter pack extends vertically beyond the uppermostedge of the filter support means, it is likely to cause interferencewhen attaching the filter support means to the coffee maker.

A particularly preferred embodiment of the present invention uses twolayers of inexpensive porous filter paper secured to one another abouttheir perimeters by a layer of polymeric material such as polyethylenewhich is melted during the assembly of the filter to bond the two filterpaper layers together. The layer of polymeric material can serve twopurposes. First, it can act as an adhesive for bonding one layer offilter paper to the other in order to contain the tea leaves within aregion, which is referred to herein as a brew chamber. Second, it candirect the brewing water through the mass of tea leaves by making thesubstantially vertically extending conformable side walls and a portionof the bottom of the brew chamber substantially impermeable to water.The maximum volume of the brew chamber formed between the unsecuredportions of the two layers of filter paper is preferably between about100 percent and about 400 percent greater than the volume of the dry tealeaves contained therein to allow the tea leaves to expand and floatwithin the chamber during steady state brewing conditions.

The layer of polymeric material would preferably be cut into a generallyannular shape which would extend over the bottom layer of filter medium,except in a portion of the area coinciding with the brew chamber, wherethe flow of brewed tea is desired. This, in essence, creates a funnelwhich not only permits flooding of the brew chamber with water, butwhich also directs the incoming hot brewing water through the brewchamber of the filter pack.

A hydrophobic adhesive which allows the use of relatively inexpensivenon-heat sealable filter mediums, such as paper, may alternatively beemployed to construct other embodiments of the present invention. Thishydrophobic adhesive would preferably be applied everywhere on thebottom layer of filter medium, except in a portion of the areacoinciding with the brew chamber, where the flow of brewed tea isdesired. This likewise creates a funnel which not only permits floodingof the brew chamber with water, but which also directs the incoming hotbrewing water through the brew chamber of the filter pack.

The porosity and size of the porous area of the bottom filter medium,where the polymeric material or adhesive is not applied, controls thedischarge flow rate of the brewed tea out of the brew chamber of thefilter pack. The porosity and size of that centrally located portion ofthe top filter medium which is not bonded to the bottom filter mediumcontrols the flow rate of incoming hot water into the brew chamber untilsuch time as the brew chamber becomes flooded. The rate at which watercan thereafter enter the flooded brew chamber is controlled by thedischarge flow rate of brewed tea from the brew chamber.

The individual coffee maker being used determines the total volume ofconcentrated tea product brewed in each batch and the flow rate of waterdelivered to the filter pack during the brewing cycle.

In some coffee makers, a portion of the hot water which ends up in thefinished batch is deliberately routed so as to completely bypass thefilter pack. In this situation, concentrated brewing of the tea iscarried out only by that portion of the hot water which is directedthrough the filter pack. The concentration of the brewed tea exiting thefilter pack is then diluted to the level desired by the consumer by thehot water which bypassed the filter pack when the tea exiting the brewchamber is collected in the pot located beneath the filter supportmeans. Systems of the aforementioned type are typically employed toreduce the overall cycle time required to brew a pot of tea.

In the absence of such a water division system, the consumer dilutes theconcentrated tea produced by the coffeemaker with the requisite amountof water to the desired concentration. Particularly when an iced teaproduct is desired, cool or cold water is used for dilution so that themelting time of the ice added is greatly extended in comparison with ascenario in which ice is added directly to freshly brewed, hot tea.

While the particular volume of the tea batch to be brewed and the flowrate of the incoming hot water into the filter pack may vary somewhatfrom one machine manufacturer to another, thereby slightly altering theabsolute brew strength of the tea produced when one manufacturer'scoffee maker is compared to another, for any given coffee maker improvedtea filter packs of the present invention will produce comparableextraction efficiencies when compared to bulk tea/paper filter systemsusing identical brewing conditions and improved pot-to-pot brew strengthconsistency when compared to conventional tea filter packs of the priorart.

Commonly assigned, co-pending U.S. patent application Ser. No.07/907761, filed Jun. 30, 1992, now U.S. Pat. No. 5,298,267 has provideda similarly improved filter pack for use with dry roast and groundcoffee. The tea filter packs according to the present inventionincorporate the teachings and features of the coffee filter packs of theaforementioned co-pending application, and in addition incorporatespecific design features to account for the differences in brewingcharacteristics between coffee and tea and the additional difficultiesencountered when using coffee brewing machines to brew tea.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified perspective view of an improved tea filter packof the present invention.

FIG. 2 is a simplified, cross-sectional view taken along section line2--2 of FIG. 1.

FIG. 2A is a simplified, cross-sectional view similar to that of FIG. 2,but showing the filter pack in the filter support means of a coffeemaker with the brew chamber of the filter pack in a fully expanded,steady state brewing condition.

FIG. 3 is a flattened planar view of bottom layer 10 of the filter packshown in FIG. 1.

FIG. 4A is a simplified perspective view of male die 60, female die 70,and a flat tea filter pack of the type shown in FIG. 1 prior to closureof the dies upon one another.

FIG. 4B is a simplified perspective view of the male and female dies ofFIG. 4A in their closed position with the tea filter pack shown in FIG.4A between them.

FIG. 4C shows the formed tea filter pack of FIG. 1 as it is emergingfrom the female die shown in FIGS. 4A and 4B.

FIG. 5 is a simplified, cross-sectional view analogous to FIG. 2 of analternative embodiment of an improved tea filter pack according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an improved tea filter pack 1 of the present invention. Thefeatures of the filter pack can best be described by looking at FIG. 2,which is a simplified cross-sectional view taken along section line 2--2of FIG. 1. The tea filter pack comprises a bottom layer 10 comprised ofa flexible porous material and a top layer 20 also comprised of flexibleporous material. The inner face 11 of bottom layer 10 is joined to theinner face 21 of top layer 20 about its perimeter by a hydrophobicadhesive coating 30. The hydrophobic adhesive coating makes the porouslayers substantially impervious to water wherever it is applied.

The combination of bottom layer 10 and hydrophobic adhesive 30 creates aflexible and conformable side wall 25 which is substantially imperviousto water. Because the combination of bottom layer 10 and hydrophobicadhesive 30 together form a substantially water impermeable side wall,top layer 20 need not extend all the way to the outer perimeter ofbottom layer 10 to render side wall 25 substantially impermeable towater. Alternatively, the bottom layer 10 could be smaller and the toplayer 20 could be rendered water impermeable by coating its outerperimeter with a hydrophobic adhesive 30. Hydrophobic adhesive coating30 is extended along the inner face 11 of bottom layer 10 to form anannular ring 15 which coincides with the interior of brew chamber 40,leaving an uncoated permeable circular area 13 at the center of bottomlayer 10. The distance to which annular ring 15 extends into brewchamber 40 controls the permeable area 13 and hence the discharge flowrate at which brewed tea is allowed to pass through the bottom layer 10.The water flow rate into brew chamber 40 is controlled by the area ofthe unsecured central portion 23 of top layer 20. Assuming layers 10 and20 are comprised of similar material, controlling the size of thepermeable areas on the top and bottom layers for a given porositycontrols the relative flow rates of liquids through the layers.

FIG. 2A is a simplified, cross-sectional view similar to that of FIG. 2,but showing the filter pack in the filter support means 75 of a coffeemaker with the brew chamber of the filter pack in a fully expanded,steady state brewing condition. Also depicted in FIG. 2A is a wirebasket 99 which is present in the filter holder of many coffee makers.This wire basket is designed to prevent a filter from pressing againstthe solid outer wall of the filter holder. This in turn prevents themoistened filter from forming a liquid impervious seal with the solidouter wall, and ensures that the entire surface of a coffee filter isavailable for filtering purposes. Some coffee makers alternativelyincorporate a series of ribs or blade-like protrusions around the insidesurface and on the bottom surface of the filter holder to accomplish thesame purpose. Since tea does not clog the pores of the filter as doescoffee, a tea filter without a flow control mechanism would allow thehot water to pass rapidly down through the brewing chamber via theentire lower surface of the filter and out through the holes in thebottom of the filter holder without allowing sufficient steeping time.

The flow rates of liquids through the layers and the height of thesubstantially vertically extending moisture impervious side wall 25 aresized and configured in filter packs of the present invention so that asteady state brewing condition is established within brew chamber 40during a substantial portion of the brewing cycle. As used herein, asteady state brewing condition is established within brew chamber 40when the brew chamber's maximum volume V₃ is filled with water and tealeaves 50, allowing the tea leaves to expand and loosely float withinthe chamber. This condition is illustrated in the cross-section of FIG.2A.

During build up to this steady state brewing condition, the flow rate F₂of incoming hot water through the permeable region 23 of the top layer20 should be greater than the maximum flow rate F₃ of brewed tea exitingthrough the permeable area 13 in bottom layer 10. Furthermore, the waterdelivery flow rate F₁ of the coffee maker to the filter pack 1 should beless than or equal to the incoming hot water flow rate F₂ into brewchamber 40. Once a steady state brewing condition is reached and waterhas built up to the level "L" in the filter pack, as shown in FIG. 2A,flow rate F₂ will take on the value of flow rate F₃, which should stillbe less than flow rate F₁. As can be seen from FIG. 2A, substantiallywater impermeable side wall 25 must be at least tall enough to captureenough of the incoming hot water that the brew chamber 40 will becomeflooded and fully expanded to achieve a steady state brewing condition.In the embodiment shown in FIG. 2A, this minimum vertical side wallheight corresponds to level "L", which represents the maximum possiblevertical expansion of porous area 23 in brew chamber 40.

The higher the substantially water impermeable side wall 25 extendsabove this minimum, the greater will be the filter pack's insensitivityto careless placement within the filter support means 75, since lack ofperfect concentricity with the filter support means will not result inan inability to retain enough hot water to establish a flooded steadystate brewing condition within the brew chamber.

As a practical matter, the vertical height of the substantially waterimpermeable side wall 25 is greater than the foregoing minimum toprevent overflow of the incoming hot water from the coffee maker (recallthat the discharge flow rate of brewed tea from the brew chamber isnormally less than the incoming flow rate of hot water to the filterpack to permit flooding of the brew chamber).

The maximum height of the substantially water impermeable side wall 25is, of course, limited by the vertical height of the filter supportmeans 75 used on the coffee makers which are to employ the filter packsin question. If the filter pack extends vertically beyond the uppermostedge of the filter support means 75, it is likely to cause interferencewhen attaching the filter support means to the coffee maker.

Applicants have learned that the difference between the inlet flow rateF₂ of the incoming hot water and the maximum outlet flow rate of brewedtea F₃ should be sufficiently great that steady state brewing condition,as shown in FIG. 2A, is reached within the brew chamber 40 relativelyearly in the brewing cycle. Most preferably this condition isestablished before more than about 50 percent of the total volume V₂ ofwater to be passed from the coffee maker through the filter pack 1 haspassed through the discharge outlet 13 in the bottom layer 10. Meetingthis condition helps ensure that filter packs of the present inventionwill consistently extract about the same level of flavor solids from apredetermined volume V₁ of tea leaves 50 as could be extracted from anidentical volume V₁ of identical bulk tea leaves brewed under identicalconditions, but using a porous paper filter containing the bulk tealeaves in an unconstrained condition. Thus, unlike prior art tea filterpacks, improved tea filter packs of the present invention delivercomparable brewing efficiency to bulk tea/filter paper systems, butwithout the need for unitized pouches of premeasured tea leaves toensure pot-to-pot brew strength consistency and without the messassociated with bulk tea and paper filters.

As shown in FIG. 3, hydrophobic adhesive coating 30, which is preferablya hot melt, is applied in a ring like fashion around the perimeter ofthe inner face 11 of bottom layer 10, leaving an uncoated porousdischarge outlet orifice 13 at the center of bottom layer 10. Apredetermined amount of tea leaves 50 having a dry volume V₁ are placedwithin the area defined by dotted line 35 either before or at the sametime as top layer 20 is superposed on bottom layer 10. Top layer 20 isthen brought into contact with bottom layer 10 and heat and pressure areapplied to only the outer perimeter of top layer 20, i.e., the areawhich lies outside dotted line 35 in FIG. 3. This adheres the outerperimeter of top layer 20 to the outer perimeter of bottom layer 10.Accordingly, dotted line 35 shows the innermost point where the toplayer 20 ceases to be adhered to bottom layer 10 and defines the inletpermeable inlet orifice 23 for entry of the incoming hot water into brewchamber 40. Dotted line 35 also defines the outermost circumference ofbrew chamber 40.

As can be discerned from FIG. 3, the surface area of the inlet orifice23 to the brew chamber 40 is larger than the surface area of thedischarge outlet orifice 13 out of the brew chamber. For any givenporosity of the top and bottom layers this will make the flow rate intothe chamber greater than the maximum flow rate out of the chamber duringbuild-up to a steady state brewing condition. This difference in flowrates in combination with the impermeable side walls of the filter pack1 causes the incoming hot water to build up and puddle inside the brewchamber 40 in the manner generally shown in FIG. 2A. This permits thetea/water exposure and contact time needed to obtain a desired brewstrength for a predetermined amount of tea. Also, allowing water tobuild up causes the tea leaves 50 to loosely float and expand inside thebrew chamber 40. This minimizes channeling of the hot water directlythrough the chamber without sufficient contact with the tea leaves,thereby increasing the efficiency of tea flavor solids extraction andreducing extraction variability from pot-to-pot.

Besides having sufficient tea/water contact time, Applicants havelearned that sufficient tea/water contact area must be provided in orderfor a predetermined amount of tea to consistently produce a desired brewstrength, i.e., the tea leaves must not be tightly constrained or theycannot float and establish a steady state brewing condition. Brewchamber 40 should be large enough to encase the desired amount of tealeaves 50 and to allow the tea leaves to expand and loosely float whenthe chamber is flooded, i.e., during steady state brewing conditions, asgenerally shown in FIG. 2A. Ideally the maximum volume V₃ of brewchamber 40 is between about 100 percent and about 400% larger than thedry tea volume V₁. A representative condition within the foregoing rangeis illustrated in the cross-section of FIG. 2.

The filter pack 1 preferably exhibits a frusto-conical shape, asgenerally shown in FIG. 1, so that even if the operator is careless ininstalling it in the filter support means or holder 75, the filterpack's shape and the conformability of its side wall 25 will tend toautomatically self align the filter pack to produce a situation similarto that shown in FIG. 2A, so that the desired funnel effect takes placeduring the brew cycle.

One method of imparting the frusto-conical shape can be explained bylooking at FIGS. 4A, 4B and 4C. A fully assembled planar filter pack 1is placed between female die 70 and male die 60 so as to take on thedesired shape as shown in FIG. 1. The unformed diameter 16 shown in FIG.4A is larger than the formed diameter 17 shown in FIG. 4C. As can beseen from FIG. 2A, the formed diameter 17 is ideally the same diameteras the bottom of the coffee filter holder 75 of the coffee maker.

The foregoing forming process allows the unadhered porous inlet portion23 of top layer 20 to puff up during brewing and create a large enoughbrew chamber 40 to achieve good tea extraction, as shown in FIGS. 2 and2A. The substantially water impermeable conformable side wall 25 ensuresthat the hot water needed for flooding of the brew chamber will beavailable no matter how sloppily the filter pack 1 is placed in thefilter holder 75. Thus, unlike filter packs of the prior art, thepresent invention is relatively insensitive to operator error.

The bottom and top layers used in filter packs of the present inventioncan be comprised of any paper, synthetic nonwoven, or plastic materialthat has a porosity and mesh size capable of preventing substantiallyall of the tea particles from entering into the brewed tea beverage orsifting out while handling the disposable filter pack before or afterbrewing.

In a particularly preferred embodiment, both layers are comprised offilter paper comprised substantially entirely of wood fiber. This is thetype of filter paper normally used to make conventional coffee filters.

The adhesive used to seal and secure the inner and outer layers to oneanother is preferably comprised of a hydrophobic hot melt materialapplied as a continuous layer, e.g., a polymeric material, such aspolypropylene, applied with a rotogravure, screen, or spray coatingsystem. The particular hydrophobic adhesive material employed should, ofcourse, be approved for direct contact with food and beverage substancesand boiling water. The adhesive ideally has a viscosity of between about500 and about 15,000 CPS at 350° F. for coating application purposes.The adhesive should also have a softening temperature greater than 180°F. in order that the seal between the filter mediums employed in thefilter pack 1 does not fail in hot water during brewing. The thicknessof the hydrophobic adhesive can be adjusted, as desired, to provide thedesired seal strength and degree of water imperviousness. The thicknessof the adhesive can also be varied within the different portions of thefilter pack to achieve different objectives. For instance, a thicknessof 0.5 mils of adhesive may be sufficient to render the conformable sidewall 25 of the filter pack substantially impervious to liquid, while a 1mil thickness of adhesive may be needed to create sufficient sealstrength.

In a preferred embodiment of the present invention, a die cut layer ofpolymeric material, such as commercially available polyethylene, wouldbe substituted for layer of hydrophobic adhesive 30. This likewisecauses the filter pack to be substantially impermeable to water whereverthe polyethylene is present. The three layers of the resultant laminatecould, of course, be adhered to one another by applying sufficient heatto soften the polyethylene. The resultant laminate tea filter pack wouldbehave identically to the embodiment shown in FIGS. 1 and 2. Such apolyethylene layer would preferably have a thickness of between about 1and about 3 mils.

In still another embodiment of the present invention, the flow rates F₂and F₃ through brew chamber 40 could be controlled by making the porousportion 13 of bottom layer 10 less porous than the porous portion 23 oftop layer 20. This is usually achieved by making the bottom layer 10slightly thicker than the top layer 20. In an embodiment of the lattertype, the hydrophobic adhesive 30 would not need to extend inwardlybeyond dotted line 35 in FIG. 3, since the difference in porosity of thelayers would produce a difference in flow rates even if their respectiveareas were identical in size.

In yet another embodiment of the present invention the layers 10 and 20could be comprised of a synthetic non-woven material containing hundredsof tiny plastic fibers packed close enough together to prevent teaparticles from entering the brewed beverage or escaping from the brewchamber, while still allowing water to pass therethrough. Materials ofthe latter type can be rendered impervious in selected regions byselectively applying heat and pressure to melt the discrete fiberstogether, thereby creating a thin film of plastic that is substantiallywater impervious. Heat and pressure could be used to adhere the twolayers employed to construct the coffee filter pack to one another inthe same areas shown in FIGS. 1, 2, and 3.

In still another embodiment of the present invention, the layers of thefilter pack can be comprised of a continuous film of plastic orpolymeric material, such as polyethylene, that is initially waterimpermeable. Water permeable regions can then be made by puncturing theplastic material and making hole sizes which are large enough to letwater pass yet small enough to prevent the passage of substantially allof the solid tea particles in the brewing chamber. This puncturingcould, if desired, be done by a water jet process of the type generallydescribed in commonly assigned U.S. Pat. No. 4,695,422 issued to Curroet al. on Sep. 22, 1987 and U.S. Pat. No. 4,609,518 issued to Curro etal. on Sep. 2, 1986 both disclosures of which are hereby incorporatedherein by reference. Alternatively, a mechanical punching process couldbe employed to perforate the film. Other suitable perforated films arecommercially available from Tredegar Industries, Film Products Division,Terre Haute, Ind.

The size and number of holes could be varied to control flow ratesthrough the filter pack. For example, more holes could be provided onthe top layer than on the bottom layer so as to make the bottom layerless porous. Furthermore, the holes could be of identical size anddensity in both layers and the flow areas adjusted in the same mannershown in FIGS. 1, 2 and 3 so as to control liquid flow rates into andout of the brew chamber in a similar fashion. That is the size of theporous inlet orifice and porous outlet orifices could be varied. Noholes would be placed in the side wall portion of the filter pack so asto keep them substantially impermeable to water.

Many of the plastic sheets described above are made in rolls or sheetsof plastic film that are apertured or water permeable continuouslythroughout. Therefore, in order to make the filter pack of the presentinvention with continuously apertured film, the top and bottom layersshould be secured together and made impermeable around the regioncorresponding to the side wall 25. This could be accomplished byapplying heat and pressure to this region to form an impermeable sidewall. Any sealing process could be used that causes the two layers ofplastic material to bond together. The sealing should cause the plasticto melt and flow back together, thereby closing substantially all of theholes therein. If the top and bottom layers are made from identicalsheets of plastic material having the same size holes and density ofholes the flow rates could be adjusted by applying heat and pressure tothe bottom layer to close up some of the holes. This reduces the size ofthe outlet orifice and thereby reduces the flow rate therethrough.

It has been found that for the plastic films described above, a holesize ranging from 4 mils to 10 mils is ideal for retaining dry teasediment in the brewing chamber. Approximately 40-100 holes, regularlyarrayed and spaced, for this size range per square inch of material isideal for obtaining the good water flow characteristics. In addition,surfactants can be applied to the plastic films to aid in water flow.The surfactants can be applied to the surface or incorporated within thematerial. Suitable surfactants for application on the films surfacewould include polysorbates, polyglycerol esters and monoglyceridederivatives.

Still yet another embodiment of the present invention is shown in FIG.5. FIG. 5 is a simplified cross-sectional view of tea filter pack 101 ofthe present invention. Tea filter pack 101 comprises bottom layer 110made from porous filter paper, and top layer 120 made from a continuousfilm of plastic material, such as those described above. When sealing acontinuously porous layer of coextruded plastic film to porous filterpaper, it is preferred that most of the heat come from the paper side.This allows the sealant side of the film to flow into the paper creatinga stronger bond, and aiding in closing the holes in the film.

It is preferred that when using a plastic film to make either or bothlayers of the tea filter pack that the plastic material used be a twolayer co-extruded plastic film wherein the sealant side of the film, thelayer that is to be sealed to another layer, has a lower meltingtemperature than the outside surface in order to aid in sealing. FIG. 5shows the top layer 120 as being a co-extruded plastic film. Top layer120 comprises two sub-layers 121 and 122. It is preferred that sub-layer121 have a lower melting temperature than sub-layer 122. This differencein temperatures allows for higher sealing temperatures to be used whilepreventing the non-sealant side of plastic material from sticking to thesealing surface. Typical materials for sub-layer 122 include polyolefinswhereas typical materials for sub-layer 121 also include polyolefins butcontaining EVA's therein. Numerals 23, 25, 40, and 50 refer tostructural elements similarly numbered in FIG. 2.

In a particularly preferred embodiment of the present invention thewater permeable region 13 of the bottom layer in the brewing chamber 40is generally located in the center of the brew chamber where the tealeaves are placed. A single continuous permeable area 13 is alsogenerally preferred over a multiplicity of discrete porous areas tomaximize consistent extraction of flavor solids from the tea leaves 50contained within the brew chamber 40.

EXEMPLARY EMBODIMENT OF THE PRESENT INVENTION

A filter pack of the type generally shown in FIGS. 1, 2 and 3 wasconstructed using a generally circular shaped piece of James River 20lb/3000 ft² basis weight porous filter paper having a 9.5 inch diameteras the bottom layer. Pierce & Steven's B7209 AE03 water-basedhydrophobic adhesive was manually pattern coated on the bottom layer inthe pattern generally shown in FIG. 3 using a small paint brush andleaving an uncoated circular central area having a 2.25 inch diameter atthe center of the bottom layer to act as the discharge flow outlet 13for brewed tea. A dose of 1 oz. of Tender Leaf Tea having a dry volumeof approximately 5 cubic inches was placed in the center of the uncoatedportion of the bottom layer.

A generally circular shaped piece of James River 20 lb/3000 ft² basisweight porous filter paper with a 9.5 inch diameter was employed for thetop layer. The top layer was concentrically centered with and heatsealed to the bottom layer to encapsulate the tea. The width of the sealextended radially inwardly from the outer perimeter of the top layer fora distance of 3 inches. This resulted in a porous inlet area 23 to thebrew chamber having a diameter of approximately 3.5 inches.

The porosity of the filter paper used to make the top and bottom layerswas approximately 300 milliliters of water/minute/in². Since the area ofthe inlet was 9.62 in², the maximum possible flow rate F₂ of hot waterinto the brew chamber was approximately 2.9 liters/minute. This flowrate is much greater than the flow rate F₁ at which most coffee makersdeliver hot water to the filter pack. Therefore the actual flow rate F₂will, in most instances, be equal to the flow rate F₁ delivered by thecoffee maker to the coffee filter pack prior to establishing a steadystate brewing condition in the brew chamber. Once a steady state brewingcondition has been established within the brew chamber, flow rate F₂will be substantially equal to the discharge flow rate F₃ of brewed teaexiting the brew chamber.

Next, the filter pack was formed, as generally shown in FIGS. 4A, 4B,and 4C to take on the desired frusto-conical shape and a bottom diameterof approximately 4.5 inches. The forming process used male and femaledies, as generally shown in FIGS. 4A-4C. The filter pack was firstcentered over the female die 70. The male die 60 was then forced downinto the female die, forming and folding the filter pack in such a waythat it was sandwiched between the male and female dies. Hot air at 200°F. was blown onto the filter pack side wall 25 to soften the hydrophobicadhesive 30. The filter pack was then cooled for 5 to 10 seconds toallow the adhesive to set to the frusto-conical shape and removed bylifting up the male die 60 and shoving the filter pack through thebottom of the female die as shown in FIG. 4C.

Seven exemplary tea filter packs of the aforementioned type were brewedusing a Bunn OL20 coffee maker having a porous filter support with abottom diameter of approximately 4.5 inches. The coffee maker deliveredapproximately 1,870 milliliters of water at 195° F. in approximately 2.5minutes, thereby resulting in an incoming hot water delivery rate F₁ ofapproximately 748 milliliters/minute. The brew chamber of the filterpack was flooded and a steady state brewing condition establishedtherein within the first 30 seconds of the brewing cycle. This occurredby the time no more than 20 percent of the total predetermined volume V₂of water delivered to the filter pack had passed through the brewchamber.

Samples of the final beverage were taken from all 7 pots of tea brewed.The amount of extractable flavor solids in each sample was measured byweighing the tea flavor solids remaining after evaporating the water inthe samples.

Out of the 7 pots, the extraction efficiency levels averaged 0.267 gramsof extracted tea flavor solids/gram of dry tea. The standard deviationfor the 7 samples was 0.0031 grams of extracted tea flavor solids/gramof dry tea.

IDENTICAL QUANTITY OF BULK TEA BREWED IN A CONVENTIONAL TENDER LEAFRECTANGULAR FILTER PACK

In a second separate experiment, 1 oz. of the same tea used in theforegoing exemplary embodiment of the present invention was brewed inthe standard Tender Leaf Filter Pack Design. This filter pack isrectangular in shape and uses conventional heat sealable filter paper(Dexter 39 68). The filter packs were made on a form/fill/seal machinewith 0.5 inch top, bottom, and fin seals. The 1 oz. Tender Leafrectangular filter packs were then placed in the same filter holders andBunn OL20 brewers used to test the exemplary embodiment of the presentinvention. Four replicates were brewed. Out of the four replicates, theextraction efficiency was 0.2321 grams of extracted tea flavorsolids/gram of dry tea with a standard deviation of 0.0031 grams ofextracted tea flavor solids/gram of dry tea.

    ______________________________________                                        SUMMARY OF THE FOREGOING EXEMPLARY                                            EXTRACTION RESULTS                                                                              Conventional                                                           Present                                                                              Rectangular                                                            Invention                                                                            Filter Pack Design                                          ______________________________________                                        Extraction   0.267    0.2321                                                  Efficiency                                                                     ##STR1##                                                                     Standard     0.0031   0.0031                                                  Deviation                                                                      ##STR2##                                                                     ______________________________________                                    

The foregoing exemplary data clearly demonstrates that the extractionefficiency of the exemplary tea filter packs of the present inventionexceeded that of the conventional filter pack design by approximately15%.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various changes and modifications can be made without departingfrom the spirit and scope of the present invention. For example, thepost fabrication forming step could be omitted, and the filter packcould remain substantially flat until insertion into the filter supportmeans of the coffee maker. Because the substantially water impermeableside walls are flexible, insertion of the substantially flat filtersupport means will cause them to conform to the filter support means andassume an upwardly directed orientation sufficient to produce thedesired brewing action. It is intended to cover in the appended claims,all such modifications that are within the scope of this invention.

What is claimed is:
 1. A conformable, high extraction efficiency, teafilter pack containing a predetermined volume V₁ of dry tea leaveshaving extractable flavor solids therein, said tea filter pack beingsuitable for use in combination with a coffee maker having a porousmeans for supporting said conformable filter pack in an upwardly concaveconfiguration and means for delivering a predetermined volume V₂ of hotwater into said upwardly concave tea filter pack at a predeterminedwater delivery flow rate F₁ to produce a brewed tea product ofsubstantially consistent brew strength from one pot to the next, saidtea filter pack comprising:(a) a bottom layer comprised of a flexiblematerial, said bottom layer having inner and outer faces; (b) a toplayer comprised of a flexible material, said top layer having inner andouter faces, said inner face of said top layer being centered andcontinuously secured to said bottom layer about said top layer's outerperimeter, thereby defining a brew chamber between their centrallylocated non-joined areas, said brew chamber containing saidpredetermined volume V₁ of dry tea leaves, said brew chamber having amaximum volume V₃ that is larger than the volume V₁ of said dry tealeaves; (c) a conformable side wall defined by the portions of said topand bottom layers extending outwardly from the outer perimeter of saidbrew chamber, said filter pack further including a means for making saidside wall substantially impervious to the passage of water, said sidewall, upon insertion into said support means in said coffee maker, beingsubstantially vertically oriented about its entire periphery so as toretain incoming hot water from the coffee maker therein, the verticalheight of said substantially water impervious vertically extending sidewall being at least sufficient to retain enough incoming hot water tototally immerse said brew chamber when said brew chamber is in itsflooded and fully expanded condition; (d) a porous inlet orifice in saidtop layer of said brew chamber to prevent the passage of tea leavestherethrough yet allow incoming hot water, which is retained by saidsubstantially vertically oriented substantially water impervious sidewall, to pass therethrough at a predetermined flow rate F₂ at leastuntil a substantially steady state brewing condition is reached insidesaid brew chamber; and (e) a porous discharge outlet orifice in saidbottom layer of said brew chamber to prevent the passage of tea leavestherethrough yet allow brewed tea to pass therethrough at apredetermined maximum outlet flow rate F₃ once a steady state brewingcondition is reached inside said brew chamber, said porous inlet orificein said top layer being of larger area than said porous discharge outletorifice in said bottom layer such that said maximum outlet flow rate F₃is less than said flow rate F₁ of said incoming hot water from saidcoffee maker and less than said inlet flow rate F₂ into said brewchamber, the difference between said inlet flow rate F₂ and said outletflow rate F₃ being sufficiently great that said brew chamber becomesflooded to produce a steady state brewing condition wherein the combinedvolume of the water and the tea leaves contained in said brew chamberare substantially equal to the maximum volume V₃ of said brew chamberbefore a significant portion of the total volume V₂ of incoming hotwater has exited said brew chamber, said maximum volume V₃ of said brewchamber being sufficient to allow said tea leaves to expand and floatwithin said brew chamber during said steady state brewing condition, andwherein said means for making said side wall substantially impervious tothe passage of water extends onto the inner face of said bottom layer insaid brew chamber.
 2. A tea filter pack according to claim 1, whereinsaid substantially water impermeable side wall is preformed to causesaid tea filter pack to assume an upwardly concave configuration priorto insertion of said tea filter pack into said support means on saidcoffee maker.
 3. A tea filter pack according to claim 1, wherein saidtop layer and said bottom layer are comprised of porous filter paper,and wherein said means for making said side walls substantiallyimpervious to the passage of water comprises a hydrophobic polymericmaterial coated on said bottom layer in all areas other than saiddischarge outlet in said bottom wall of said brew chamber.
 4. A teafilter pack according to claim 3, wherein said top layer is alsocomprised of porous filter paper and wherein said porous inlet orificein said top layer of said brew chamber comprises the centrally locatednon-joined portion of said top layer.
 5. A tea filter pack according toclaim 4, wherein said top layer and said bottom layer are continuouslysecured to one another about said top layer's outer perimeter byapplying heat and pressure to said top and bottom layers to soften saidhydrophobic polymeric material on said bottom layer and cause it to bondsaid layers to one another upon cooling.
 6. A tea filter pack accordingto claim 5, wherein said hydrophobic polymeric material comprises a hotmelt adhesive.
 7. A tea filter pack according to claim 1, wherein saidtop and bottom layers are both comprised of identical porous materialand said flow rates F₂ and F₃ are controlled by making the porousdischarge outlet orifice in said bottom layer of said brew chambersmaller in size than the porous inlet orifice in said top layer of saidbrew chamber.
 8. A tea filter pack according to claim 1, wherein saidmeans for making said side wall substantially impervious to the passageof water comprises a substantially water impermeable polymeric layerlocated between said top layer and said bottom layer and secured to saidbottom layer, said polymeric layer including a centrally locatedaperture which defines said porous discharge orifice in said bottomlayer of said brew chamber when said polymeric layer is secured betweensaid top and said bottom layers.
 9. A tea filter pack according to claim1, wherein said flow rate F₂ of said porous inlet orifice and saidmaximum flow rate F₃ of said porous discharge outlet orifice are sorelated that a steady state brewing condition is established in saidbrew chamber before no more than about 50 percent of said volume V₂ ofincoming hot water has exited said brew chamber.
 10. The tea filter packof claim 9, wherein said inlet flow rate F₂ of said porous inlet orificeis between about 1.5 and about 2.0 times said maximum discharge flowrate F₃ of said porous discharge orifice.
 11. A tea filter packaccording to claim 1 or claim 2, wherein the vertical height of saidsubstantially water impermeable vertically extending side wall isslightly less than the minimum vertical height of said porous filtersupport means on said coffee maker.